Implement mercurial detection on the agents When agent starts, hg-plugin detects installed hg (searches it in the $PATH). If plugin is able to run hg and hg has an approrpiate version (1.5.2+), then plugin reports path to hg in the 'teamcity.hg.agent.path' parameter. This parameter can be used in the "HG command path" field in a VCS root settings, configurations with such root will be run only on agents which report path to hg. Also user can set this parameter manually in the buildAgent.properties. A server side of plugin first checks value of internal property 'teamcity.hg.server.path' and if property is set, its value is used. Second, plugin tries to use path from the settings of VCS root: if path is equal to '%teamcity.hg.agent.path%' - use 'hg' as path, otherwise use a value from the root. With such order old setups, where path in the VCS root was used on both server and agent, will continue to work. New VCS roots with references in the path will also work if hg is in the $PATH on the server or internal property is set.